Research Activities

Environmental fluid mechanics is the study of principles of fluid mechanics and their application for the identification, investigation, and solution of environmental problems.  Water Environment Modeling is about the formulations and applications of mathematical models that simulate water flow and chemical transport in rivers, lakes, groundwater, estuaries, coastal, and ocean waters. These models are used to evaluate the response of water environment to human interventions and serve as useful analytical tools for water pollution control and resource management. Dr. Liu has been engaging research on this area since late 1970s when he was a senior Hydraulic Engineer/senior research scientist in New York State Department of Environmental Conservation. Model parameters estimation is an important part of modeling. Over the years, laboratory and field studies have been conducted by Dr. Liu and his colleagues to develop consistent and accurate methods for estimating model parameters such as dispersion coefficient and reaeration coefficient under varying environmental conditions. 

   Representative Publications:   

1. Liu, C.C.K., Lin, P., and Xiao, H. (2022). Water Environment Modeling, CRC Press Taylor & Francis Group. London. 
2. Liu, C.C.K. (2004). Calibrating Steady-state Water Quality      Models with Field Data, Chapter 5-1, In: Environmental Hydraulics and Sustainable Water Management,      Taylor & Francis Group, London, pp. 665-670.
3. Shen, H.H., Cheng, A.H.D., Wang, K., Teng, M.H.,      Liu, C.C.K. (ed.) (2002) Environmental Fluid Mechanics: Theories and      Applications, ASCE book, American Society of Civil Engineers (ASCE).
4. Liu, C.C.K. (1986). Surface Water Quality Analysis, Chapter 1 In: Wang, L and Pereira, N.C. (ed.), Handbook of Environmental Engineering, The Humana Press,      pp.1-59.
5. Liu, C.C.K. and Fok, Y.S. (1983). Stream Waste Assimilative Capacity Analysis Using Reaeration Coefficients Measured by Tracer Techniques. Water Resources Bulletin, J. American Association of Water Resources (AWRA), 19(3):439-445. 

Systems modeling approach was introduced by Volterra (1959) to simulate electromagnetic and elastic processes with an infinite power series of integral equations. A system is linear if the superposition principle is valid such that the response of a system to two or more inputs is the sum of the responses of the system to each input individually. According to the linear systems theory, a linear system model can be simulated by truncating Volterra integral series into a simple convolution integral. In water environment modeling, linear systems model was first applied for watershed rainfall-runoff analysis.  Later, Dr. Liu proposed the application of linear systems models for the simulation of contaminant transport in upper soils. He submitted a proposal to the US Geological Survey in 1987, entitled "Compatibility of Physically Based and Linear System Solute Transport Modeling Approaches and Their Conjunctive Application".  His project and 34 others were selected for funding from among 275 proposals submitted in an open national competition. Dr. Liu also applied the linear systems theory for river water quality modeling. Results of his linear systems river water quality modeling were published in an ASCE book “Environmental Fluid Mechanics - Theories and Application”; a corresponding user manual was published as a technical report of University of Hawaii Water Resources Research Center. 

   Representative Publications:   

1. Liu, C.C.K. and Neill, J.J. (2002). Linear Systems Approach to River Water Quality Analysis, Chapter 12 in ASCE Book: Environmental Fluid Mechanics – Theories and Application, American Society of Civil Engineers (ASCE), pp.421-457.
2. Liu, C.C.K. and Neill, J.J. (2000). Linear Systems Approach to River Water Quality Analysis: Computer Program Documentation and User Manual, Project Report PR-20000-05, Water Resources Research Center, University of Hawaii at Manoa.
3. Liu, C.C.K. (1988). Solute Transport Modeling in Heterogeneous Soils: Conjunctive Application of Physically Based and Linear System Approaches. J. Contaminant Hydrology, 3:97-11.
4. Liu, C.C.K. and Feng, J.S. (1988). Chemical Residue Transport in Aggregated Soils: A Mathematical Simulation by the Linear System Approach, Technical Report No.179, Water Resources Research Center, University of Hawaii at Manoa, 46p.
5. Liu, C.C.K. and Brutsaert, W.H. (1978). A Nonlinear Analysis of the Relationship between Rainfall and Runoff for Extreme Floods, J. Water Resources Research, 14)1):75-88. 

Comprehensive numerical groundwater modelswhich simulate both flow and salinity transport processes in coastal basal aquifers in Hawaii have been developed and applied by Dr. Clark C.K. Liu and other researchers at University of Hawaii. Although these modeling efforts have enhanced our understanding of basal aquifers, they have not yet become viable management tools because of the difficulties encountered in model parameters estimation, model calibration and verification. A simple robust analytical groundwater flow model (RAM) with sharp interface assumption was first developed by Mink in 1980s. Later RAM was modified by Liu to include the processes of salinity transport and is called as RAM2. The determination of the values of two principal parameters of a basal aquifer ie., mean residence time and dispersion coefficient were successfully determined based on deep monitoring well data. RAM and RAM2 are being used by the Hawaii Water Resources Commission for the determination of the sustainable yields of individual Hawaii basal aquifers. 

   Representative Publications:   

1. Liu, C.C.K. and Dai, J. (2012). Seawater Intrusion and Sustainable Yield of Basal Aquifers, J. American Association of Water Resources (AWRA), 48(5):861-870.
2. Liu, C.C.K. (2008). RAM2 Modeling and the Determination of Sustainable Yield of Hawaii Basal Aquifer, Project Report PR-2008-06, Water Resources Research Center, University of Hawaii, 81p. https://files.hawaii.gov/dlnr/cwrm/publishedreports/PR200806.pdf
3. Liu, C.C.K., Ice, C., Levy, J.K., and Moncur, J. (2005). Institution, Policies, and Technologies for sustainable Watershed Management in the Asia-Pacific, Water Resources Impact, American Water Resources Association (AWRA), 7(2): 6-9.
4. Lin, P., Liu, C.C.K., Green, R., and Schneider, R. (1995). Simulation of 1, 3 dichloropropene in Topsoils with Pseudo First-order Kinetics, J. Contaminant Hydrology, 19: 307-317.
5. Liu, C.C.K., Ewart, C. and Huang, Q. (1991). Response of a Basal Water-Body to Forced Draft, In ASCE Book: Ground Water in the Pacific Rim Countries, J. Peters (ed.), American Society of Civil Engineers (ASCE), pp.36-42.
6. Liu, C.C.K., Lau, L.S. and Mink, J.F. (1983). Groundwater Model for a Thick Freshwater Lens. J. Ground Water, 21(3):293-300. 

Deep ocean water (DOW) at 300 meters or below is cold, nutrient-rich and free from pathogenic bacteria. Over the past decades, technological advancements were achieved for applying DOW as a natural resource. One such advancement was ocean thermal energy conversion (OTEC). Looking to the future, greater potential of DOW application can be realized for open ocean mariculture. Research on artificial upwelling and mixing (AUMIX 奧袐‌) which is essential for the development of DOW-enhanced open ocean mariculture has been conducted at University of Hawaii since 1992. Mathematical modeling plus laboratory and field experiments of this research generated the following results: (1) a wave-driven artificial upwelling device was developed and tested, and (2) the discharge of upwelled deep ocean water and the formulation of nutrient-rich DOW plumes in the open ocean were tested. Based on this research and related research conducted by other institutes, it is clear that desirable nutrient-rich DOW plumes can be established and maintained within the biologically productive zone in the open ocean. 

 Representative Publications:   

1. Liu, C.C.K. (2018). Ocean thermal energy conversion and open ocean mariculture: The prospect of Mainland-Taiwan collaborative research and development, J. Sustainable Environmental Research, 28:267-273.
2. Fan, W., Pan, Y., Liu, C.C.K., Wiltshire, J.C., Chen, C.A., and Chen, Y. (2015). Hydrodynamic design of deep ocean water discharge for the creation of a nutrient-rich plume in the South China Sea, J. Ocean Engineering, 108:356-368.
3. Liu, C.C.K., Sou, I.M., and Lin, H. (2003). Artificial upwelling and near-field mixing of a nutrient-rich deep-ocean water plume, Journal of Marine Environmental Engineering, 7(1): pp.1-14.
4. Liu, C.C.K. (1999). Research on Artificial Upwelling and Mixing at the University of Hawaii at Manoa, IOA Newsletter, International OTEC/DOWA Association, 10(4): pp.1-8.
5. Liu, C.C.K., and Jin, Q. (1995). Artificial Upwelling in Regular and Random Waves, J. Ocean Engineering, 22(4):337-350.
6. Liu, C.C.K., Lin, H and Guo, F. (1998). Wave-Driven Artificial Upwelling: Hydraulic Modeling and Empirical Equation, Proceedings of the ASCE 12thEngineering Mechanics Conference, La Jolla, CA, American Society of Civil Engineering (ASCE), pp.1569-1572. 

Water desalination driven by renewable energy is an attractive alternative of providing freshwater supply to coastal and other remote communities. A renewable-energy-driven desalination system was developed by the University of Hawaii at Manoa with funding support by U.S. National Science Foundation (NSF) and by U.S. Bureau of Reclamation (USBR). This system consists of (1) a wind-driven pumping subsystem, (2) a pressure-driven membrane water processing subsystem, and (3) a solar-driven feedback control module. The system was tested by pilot experiments. Test results indicated that the system operated under mild wind speeds of 3 m/sec or higher, could reduce the salinity of feedwater from total dissolved solids (TDS) of over 3,000 mg/L to a TDS of 200 mg/L or less. The overall average rejection rate was about 94%, and the average recovery ratio was about 25%.  

   Representative Publications:   

1. Liu, C.C.K. (2013). Renewable-Energy-Driven reverse osmosis system for water desalination and aquaculture production, J. Integrative Agriculture, 12(8):1357-1362.
2.  Liu, C.C.K.  (2009). Wind-Powered Reverse Osmosis Water Desalination for Pacific Islands and Remote Coastal Communities, Desalination and Water Purification Research and Development Report No. 128, U.S. Bureau of Reclamation (USBR).  
3.  Liu, C.C.K., Xia, W. and Park, J.W., (2007).A Wind-driven Reverse Osmosis System for Wastewater Reuse and Nutrient Recovery, J. Desalination, 202(1):24-30.
4. Qin, G., Liu, C.C.K., Richman, N.H. and Moncur, J.E.T. (2005). Aquaculture Wastewater Treatment and Reuse by Wind-driven Reverse Osmosis Membrane Technology, J. Aquaculture Engineering, 32:365-378. 
5. Liu, C.C.K. Park, J. W., Migita, J. and Qing, G. (2002). Experiments of a prototype wind-driven reverse osmosis desalination system with feedback control, J. Desalination, 150 (3):277-287.
6. Liu, C.C.K. and Park, J.W. (2002). Water Desalination, McGraw-Hill Encyclopedia of Science & Technology, Ninth Edition, Volume 22, the McGraw-Hill, New York, pp.404-406, http://accessscience.com/content/Water-desalination/598900